Public property instantiation JS

// class product
var Product = function(product) {
    //this.title = product.title;
    //this.price = product.price;
   this.id = Object.getPrototypeOf(this).id++;
};

// static member - shared between object constructor and inherited in instances
Product.prototype.id = 0;

// nethod on class = static method

Product.unique_id = function() {
    return Product.prototype.id++;
};

/* Simple test methods both on instance and static */

var p1 = new Product();
var p2 = new Product();
console.log(p1.id);
console.log(p2.id);

console.log("Call 1: " + Product.unique_id() + "// 2");
console.log("Call 2: " + Product.unique_id() + "// 3");
console.log("Call 3: " + Product.unique_id() + "// 4");

/* end of tests */

var p1 = new Product({
    title: 'Keyboard',
    price: 10500
});

//p1.id(); // returns it's id